Evolving Foldable OLED Smartphone Displays

Complexity in In-fold and Out-fold Design

The Galaxy Fold at IFA - Image:Meko
The Galaxy Fold at IFA - Image:Meko

Samsung Electronics re-launched its Galaxy Fold smartphone at IFA 2019 in September.

Sweta Dash is the founding president of Dash-Insights, a market research and consulting company specializing in the display industry. For more information, contact sweta@dash-insights.com or visit www.dash-insight.com

Analyst Comment

I had the chance to have a short look at the Galaxy Fold at IFA. The sample I saw looked very good although where the fold was seemed clear – although the display performance was not compromised – it was slightly different reflections, I think – but it was only a quick look. I would still be very nervous paying so much for a device that could be easily damaged in the pocket if it is closed with something in between the two halves. Two of my photos are below. (BR)

Other brands have also joined in to introduce many different design concepts of foldable smartphones with OLED display in different sizes and formats.

Foldable smartphones and 5G-technology received strong attention at IFA as high transmission speed and low latency are expected to drive innovative products and boost demand in a slow smartphone market. There are still many issues that need to be resolved before consumer acceptance – extremely high prices, no standardization in design, robustness and durability. Innovations in the display materials and processes will continue to bring better products and reduce costs.

Many designs, sizes and prices

Royole’s FlexPai has the distinction of being the first foldable smartphone to be introduced at the end of 2018 at around $1,300 price. Samsung introduced the Galaxy Fold in early 2019, but delayed shipments due to some hinge and film issues; then the firm reintroduced it again with a new version at IFA this month. Samsung’s Galaxy fold is a 5G foldable (AMOLED) product with a front cover 4.6” display and 7.3”main display and expected to be priced around $2000 (I was told €2,100 at IFA – Editor).

The Huawei Mate X is a 5G foldable OLED smartphone that has an 8” main display that can fold to 6.6” on the front side and 6.38” display on the back with an expected price of $2600. Other smartphone suppliers such as TCL, Oppo, Vivo, Xiaomi, and Lenovo are expected to introduce their products in the future. Apple has not announced any plan for foldable iPhones, but is expected to make an introduction in 2020. With very high prices, a lack of standardization, and concerns about durability, foldable smartphone products will have very limited shipments in 2019.

Higher requirements for displays

Commercialization of foldable smartphones up to now has been based on foldable AMOLED (active matrix organic light emitting diode) display technology. For a foldable display, all the layers within the panel should be foldable, durable, and transparent with a total bending radius of less than 1.5 mm. That is why new components are needed for foldable OLEDs. Foldable requirements are as follows:

  • Cover windows need to have hybrid organic/inorganic coating on transparent polyimide (PI)
  • Polarizer needs to be thin and bendable
  • Flexible touchscreen needs non ITO materials such as silver nanowire or metal mesh
  • Need for Flexible Adhesive OCA/OCR
  • Reliability (to withstand more than 200K times bending/folding).

Bendability has a trade off with durability and robustness. Bending of a very thin film after a certain point can generate a crease or lead to deformation. The display industry has developed numerous materials and processing challenges to balance bendability with durability. However significant challenges still remain.

Complexity in In-fold and Out-fold Design

New designs for foldable smartphones still have many issues with foldable hinges, flexible covers, increased thickness and bulkier designs. Samsung’s Galaxy Fold is in-fold design while Royole’s FlexPai and Huawei’s Mate X are out-fold. Xiaomi’s future product is expected to be be based on a double-fold concept. Lenovo’s future product is expected to fold vertically in the middle. Samsung is apparently working on out-folding and vertically mid-folding designs to introduce in the near future.

The in-fold design has the advantage of better protection of the inner display, but there are disadvantages from having two displays, including a need for higher battery capacity, higher thickness and may be even higher costs.

Out-fold designs have the advantage of single display for both a phone cover and tablet display, but the disadvantage of the display screen being exposed to the outside, so it is easy to scratch or damage. Therefore a foldable cover window has to be integrated with a scratch or abrasion resistant function. More

By https://www.displaydaily.com